The present invention relates to a method and apparatus for correcting the astigmatic refractive error in the cornea of the eye. In particular, the cornea is modified by forming a flap in the cornea and exposing a portion of the cornea underlying the flap. The exposed portion is marked and an asymmetric inlay having a thin removable, transparent sheet with markings indicated thereon is positioned on the exposed portion of the cornea. The markings on the cornea and those on the sheet are aligned to ensure proper positioning of the asymmetric inlay.
A normal emetropic eye includes a cornea, a lens and a retina. The cornea and lens of a normal eye cooperatively focus light entering the eye from a far point, i.e., infinity, onto the retina. However, an eye can have a disorder known as ametropia, which is the inability of the lens and cornea to focus the far point correctly on the retina. Typical types of ametropia are myopia, hypermetropia or hyperopia, and astigmatism.
A myopic eye has either an axial length that is longer than that of a normal emetropic eye, or a cornea or lens having a refractive power stronger than that of the cornea and lens of an emetropic eye. This stronger refractive power causes the far point to be projected in front of the retina.
Conversely, a hypermetropic or hyperopic eye has an axial length shorter than that of a normal emetropic eye, or a lens or cornea having a refractive power less than that of a lens and cornea of an emetropic eye. This lesser refractive power causes the far point to be focused behind the retina.
An eye suffering from astigmatism has a defect in the lens or shape of the cornea. Therefore, an astigmatic eye is incapable of sharply focusing images on the retina.
Optical methods are known which involve the placement of lenses in front of the eye, for example, in the form of eyeglasses or contact lenses, to correct vision disorders. A common method of correcting myopia is to place a xe2x80x9cminusxe2x80x9d or concave lens in front of the eye to decrease the refractive power of the cornea and lens. In a similar manner, hypermetropic or hyperopic conditions can be corrected to a certain degree by placing a xe2x80x9cplusxe2x80x9d or convex lens in front of the eye to increase the refractive power of the cornea and lens. Lenses having other shapes can be used to correct astigmatism. The concave, convex or other shaped lenses are typically configured in the form of glasses or contact lenses.
Although these optical methods can be used to correct vision in eyes suffering from low myopia, or in eyes suffering from hypermetropic, hyperopic or astigmatic conditions which are not very severe, these methods are ineffective in correcting vision in eyes suffering from severe forms of ametropia.
However, surgical techniques exist for correcting these more severe forms of ametropia to a certain degree. For example, in a technique known as myopic keratomileusis, a microkeratome is used to cut away a portion of the front of the live cornea from the main section of the live cornea. The cut portion of the cornea is frozen and placed in a cryolathe where it is cut and reshaped. Altering the shape of the cut portion of the cornea changes the refractive power of this cut portion, which thus affects the location at which light entering the cut portion of the cornea is focused. The reshaped cut portion of the cornea is then thawed and reattached to the main portion of the live cornea. Hence, it is intended that the reshaped cornea will change the position at which the light entering the eye through the cut portion is focused, so that hopefully the light is focused directly on the retina, thus remedying the ametropic condition.
The myopic keratomileusis technique is known to be effective in curing myopic conditions within a high range. However, the technique is impractical because it employs very complicated and time consuming freezing, cutting and thawing processes.
Keratophakia is another known surgical technique for correcting severe ametropic conditions of the eye by altering the shape of the eye""s cornea. In this technique an artificial, organic or synthetic lens is implanted inside the cornea to thereby alter the shape of the cornea and thus change its refractive power. Accordingly, as with the myopic keratomileusis technique, it is desirable that the shape of the cornea be altered to a degree that allows light entering the eye to be focused correctly on the retina.
However, the conventional lenses and methods for type of correction are often impractical for correcting astigmatic error in the eye. Since an irregular shaped cornea or eye generally causes astigmatic error, to correct astigmatism an implanted lens must be a specific asymmetrical shape that would negate the irregularity. Often is difficult to properly position and maintain the lens in the correct orientation relative to the cornea, thereby making the procedure difficult and time consuming.
Examples of known techniques for modifying corneal curvature, such as those discussed above, are described in U.S. Pat. No. 4,994,058 to Raven et al., U.S. Pat. No. 4,718,418 to L""Esperance, U.S. Pat. No. 5,336,261 to Barrett et al., and a publication by Jose I. Barraquer, M.D. entitled xe2x80x9cKeratomileusis and Keratophakia in the Surgical Correction of Aphakiaxe2x80x9d. The entire contents of each of these patents are incorporated herein by reference.
Surgical techniques involving the use of ultraviolet and shorter wavelength lasers to modify the shape of the cornea also are known. For example, excimer lasers, such as those described in U.S. Pat. No. 4,840,175 to Peyman, which emit pulsed ultraviolet radiation, can be used to decompose or photoablate tissue in the live cornea so as to reshape the cornea.
Specifically, a laser surgical technique known as laser in situ keratomileusis (LASIK) has been previously developed by the present inventor. In this technique, a portion of the front of a live cornea can be cut away in the form of a flap having a thickness of about 160 microns. This cut portion is removed from the live cornea to expose an inner surface of the cornea. A laser beam is then directed onto the exposed inner surface to ablate a desired amount of the inner surface up to 150-180 microns deep. The cut portion is then reattached over the ablated portion of the cornea and assumes a shape conforming to that of the ablated portion.
However, because only a certain amount of cornea can be ablated without the remaining cornea becoming unstable or experiencing outwardbulging (eklasia), this technique is not especially effective in correcting very high myopia or large astigmatic error. That is, a typical live cornea is on average about 500 microns thick. The laser ablation technique requires that at least about 200 microns of the corneal stroma remain after the ablation is completed so that instability and outwardbulging does not occur. Hence, this method typically cannot be effectively used to correct high myopia or large astigmatic error, because, in order to reshape the cornea to the degree necessary to alter its refractive power to sufficiently correct the focusing of the eye, too much of the cornea would need to be ablated.
Other techniques exist for correcting astigmatic error using markings on a lens. However, these techniques generally only have a mark or multiple marks on a portion of the lens. This type of marking may indicate what direction the lens should be implanted in the cornea; however, they generally do not do not indicate where on the cornea they should be placed. For example, astigmatic correction is a relatively precise procedure and the lens must be placed both centrally on the cornea or at least in a predetermined position and oriented radially in the correct position, to negate the asymmetric shape of the cornea. The conventional procedures do not allow the proper alignment of the cornea surface and the lens implanted thereon. Therefore, existing procedures are inadequate to correct astigmatic error. Furthermore, many of these procedures have permanent markings on the lens, which may hinder the sight of the patient.
Therefore, it is apparent that a need therefore exists for improved methods for further modifying the cornea to better correct ametropic conditions, and more specifically to correct astigmatic error.
Accordingly, it is an object of the present invention to provide a method for adjusting the shape of a live cornea to correct high ametropic conditions.
Another object of the invention is to provide a method for modifying the shape of a live cornea to correct astigmatic conditions.
Yet another object of the present invention is to provide a method for adjusting the shape of a live cornea to correct astigmatic conditions by aligning the inlay with markings on the cornea.
Still another object of the present invention is to provide an intracorneal inlay having removable alignment markings thereon.
Still yet another object of the present invention is to provide an intracorneal inlay for correcting the refractive error in the eye having a removable, pliable sheet with markings thereon overlying at least a portion of the inlay to indicate the alignment of the inlay.
Further still it is another object of the present invention to provide an inlay for correcting the refractive error in the eye that is positioned under a flap in the cornea and aligned with markings on an exposed surface of the cornea.
The foregoing objects are basically attained by a method of correcting refractive error in the cornea of an eye, comprising the steps of marking at least one axis on the surface of the cornea, separating a portion of the cornea, forming a first anterior facing surface and a second posterior facing surface, positioning a inlay having at least one axis indicated on the surface thereof between the first and second surfaces, and aligning the at least one axis on the inlay with the at least one axis on the surface of the cornea.
The foregoing objects are further attained by an inlay for correcting the refractive error in the cornea of the eye, comprising a first surface for placement onto an exposed surface of the cornea, a second surface opposite the first surface, and a removable sheet of material overlying the second surface, the sheet having markings thereon for accurately positioning the inlay on the exposed surface of the cornea.
Other objects, advantages, and salient features of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.